In recent years, lead storage batteries are once again in the spotlight as smart power, based on the improvement of the charge and discharge properties thereof, in the industrial field where expensive lithium ion secondary batteries make no business sense. The foregoing industrial field is not the field where lead storage batteries are used in portable devices, and refers to the field of special electric vehicles such as electric carts and forklifts in which the recycling of the lead storage batteries themselves or the devices containing such lead storage batteries is satisfactory.
The electric vehicles described above need to efficiently charge the lead storage batteries by leveraging the short down time (for example, while the passengers are playing golf in the case of electric carts used in golf courses, and while the operator is having a meal or a drink in the case of forklifts used for carrying cargo) of the user (driver). Thus, considered may be utilizing the technology (for example, Patent Document 1) of increasing the SOC (State Of Charge) based on a multi-stage constant current charge of three stages or more (charging current when the number of charging stages is n stages will be I1>I2> . . . >In−1) of decreasing the charging current upon reaching a predetermined voltage V1 and proceeding to the charging of the subsequent stage, and performing the final-stage charging for a predetermined time after the lead storage battery reaches the voltage V1. It is considered that the method of using this technology and performing a quick charge with a relatively large current in the initial stage of the multi-stage constant current charge during the short down time, and obtaining a full charge through all stages of the multi-stage constant current charge after the completion of operation.
However, in cases of using a lead storage battery as the main power source of a special electric vehicle that is basically not equipped with an auxiliary power source and repeating the charge and discharge process, unlike a vehicle equipped with an auxiliary power source, it is now known that the charging method giving consideration to a quick charge as with Patent Document 1 will result in insufficient charging, and there are cases where the life property of the lead storage battery will deteriorate.
Patent Document 1: Japanese Patent Application Publication No. 2000-243457